In an amplifier of this type, e.g. as disclosed in my copending application Ser. No. 024,077 filed Mar. 26, 1979, one of the transistors of the final stage (referred to hereinafter as the first output transistor) has an emitter forming a junction with a collector of the other transistor of that stage (referred to hereinafter as the second output transistor) whose emitter, like that of the associated pilot transistor, is connected to a usually grounded terminal of a direct-current supply having another terminal tied to the collector of the first output transistor. The latter terminal is also connected, via a diode energized in the forward direction and a constant-current source, to the collector of the pilot transistor and, via the forward resistance of another diode, to the collector of a control transistor whose base is connected to that constant-current source and whose emitter is tied to the aforementioned junction. The control transistor drives the first output transistor into maximal conduction when the resistance of the pilot transistor is high, i.e. during alternate half-cycles of an a-c input signal. When the pilot transistor saturates during the remaining half-cycles of that input signal, the second output transistor is also driven into saturation.
The current/voltage characteristic of such an a-c amplifier is nonlinear for load currents of a magnitude below a so-called quiescent current.
The first output transistor may be completely cut off or conduct at a level below its quiescent current during the operating half-cycles of the second output transistor, thus giving rise to a distortion of the load current at the beginning of its own operating cycle. This distortion, which involves the generation of higher harmonics liable to interfere with nearby high-frequency equipment, is due to the delaying effect of capacitances in the driving circuit of the first output transistor, e.g. the equivalent capacitance of a diode inserted in the base/emitter circuit of the control transistor. Such a diode, designed to stabilize the amplifier against spontaneous oscillations as needed especially in integrated circuitry, lies in parallel with the base/emitter path of the control transistor whose own equivalent capacitance is thus added to that of the diode.